The objective of the proposed project is to build and characterize a scintillator imaging array based on strontium iodide. This recently discovered scintillator offers much higher light output than any other scintillator that has been used for SPECT, while also offering high stopping power at photon energies relevant for SPECT. Recent developments in SPECT, including innovation in collimation schemes and construction of dedicated cardiac and preclinical imaging systems, have created interest in imaging detectors offering better performance than the conventional Anger Camera, which consists of a large-area sodium iodide crystal coupled to an array of discrete photomultiplier tubes. A strontium iodide imaging detector is expected to offer a significant improvement in energy resolution over the Anger Camera due to the much higher light output of strontium iodide. We anticipate an energy resolution of better than 5% at 140 keV, which is approximately a factor of two better than the typical Anger Camera. Improvements in energy resolution would allow for narrower energy windows to be applied, reducing the number of scattered photons included in the image and thereby providing improved image contrast and better quantitative accuracy. Further, improvements in energy resolution would translate into better dual-isotope SPECT capability. Because light output is an important contributor to spatial resolution as well, strontium iodide also offers the potential for better spatial resolution than sodium iodide. Our strategy is to construct an imaging detector consisting of a monolithic strontium iodide crystal, minimizing the demands on crystal packaging. The crystal will be read out using current state-of-the-art silicon photomultiplier arrays, which offer high photon detection efficiency over strontium iodide's emission spectrum. We will measure properties important to imaging performance, including spatial resolution, energy resolution, detection efficiency, count-rate capability, and uniformity.